1. Field of the Invention
The present invention is directed to a method and apparatus for digitally delaying an ultrasound signal upon reception thereof, and in particular to such a method and apparatus for use with a phased-array consisting of a plurality of ultrasound transducer elements.
2. Description of the Prior Art
The delay of ultrasound echoes is one of the crucial problems in medical ultrasound technology. Analog method and devices are known such as, for example, LC lines, mixed technologies, and CCD elements have heretofore been preferred for use at the receive side of the system. Digital delay methods are generally used only at the transmit side of the system.
A complicated delay technique is necessary, particularly given phased array devices having dynamic focussing of the reception focus over many focus locations. Relatively long delay times of up to, for example, 20 .mu.s are standard for the sweep of the ultrasound signal. The curvature of the antenna, which differs dependent on the received focus location, is achieved by finer delay steps between adjacent transducer elements. The image quality of a displayed ultrasound image is improved, as is the sharpness of the representation, as one better succeeds in setting and observing computationally identified delay times. Time differences of only about 50 or 33 nsec are usually realizeable due to the clock signal of, for example, 20 or 30 MHz prescribed in the ultrasound apparatus.